Osseointegration is defined clinically as the process whereby clinically asymptomatic rigid fixation of alloplastic materials is achieved and maintained in bone during functional loading. Discussion of this process is set out in the paper of Albrektsson, T. A multicenter report on osseointegrated oral implants. The Journal of Prosthetic Dentistry. Vol. 60, No. 1, pp. 75-84, 1988. Typical dental implants, when osseointegrated in the upper or lower jaw, provide stable anchorage for dental prostheses. One of the factors limiting the success of osseointegration is the quantity of host bone stock available at a given site. If a site has inadequate host bone it may not be possible to use typical implants, alternatively, the site will require augmentation. Need to generate bone volume may arise from different circumstances. The bone may have been inadequately formed at birth and thus there is a need to build up bone tissue to bring the bone structure closer to the norm. Bone may also have been lost as a result of trauma, disease or other factors. Sites with inadequate bone volume have heretofore been augmented in a variety of ways:
with autogenous bone grafted from a distant site in the body; PA1 with freeze-dried allogeneic bone from a bone bank, or PA1 with bone substitutes such as coral granules or hydroxyapatite crystals.
Autogenous bone grafts have no risk of rejection or viral infection and provide vital progenitor cells. However, they usually require a general anesthetic and are accompanied by some degree of morbidity which may be unacceptable to the mammal involved, particularly where the patient is human. Freeze-dried bone is easily available but is unpredictable in its behaviour because it is devoid of vital progenitor cells, bone morphogenic protein, and other factors such as TG beta. It also carries with it the risk of viral transmission. Bone substitutes have similar problems.
Thus, in many cases there is a need to generate adequate bone volume at a particular site in the body. The present invention deals with a method and equipment to generate bone volume at a particular site. While the technique is applicable to increasing bone volume at any site in the body, the need for increased bone volume often arises in connection with the jaw of a human being. Where teeth have been lost through trauma, there is often accompanying damage in the upper or lower jaw bone. In many such cases, it will be desirable to use dental implants to anchor dental prostheses.
Heretofore, bone grafting, irrespective of source, has been carried out either prior to or concurrently with the placement of a dental implant when it is necessary to build up tissue of the upper or lower jaw. In either case, the procedure usually employs a membrane such as that sold under the trade mark GORTEX in a process called guided bone regeneration (GBR). While most configurations of bony defects are amenable to augmenting with GBR, it is widely acknowledged that defects in a jaw bone which are vertical in nature, in particular, are difficult to overcome.
A process called distraction osteogenesis was first described by Codivilla in 1904. The technique became popularized and was studied extensively by Ilizarov beginning in 1951. See in particular, the following publications of Ilizarov which also describe the work of Codivilla. Ilizarov, G. A. The tension-stress effect on the genesis and growth of tissues: Part 1. The influence of stability of fixation and soft tissue preservation. Clinical Orthopaedics and Related Research. Nr. 238, pp. 249-285, 1989 and Ilizarov, G. A., The tension-stress effect on the genesis and growth of tissues: Part II. The influence of the rate and frequency of distraction. Clinical Orthopaedics and Related Research. Nr. 239, pp. 263-285, 1989. In this process, growth of bone and healing of bone defects can be stimulated by pulling apart, or distraction, of bone segments. Ilizarov discovered that a cortical osteotomy, or corticotomy, which preserves the bone's medullary blood supply and preserves the overlying periosteum, when combined with slow distraction, permitted bone lengthening without a bone graft. More recently work has been carried out on dogs. This work has demonstrated that a vertical defect of a residual alveolar ridge of a jaw bone can be corrected using osseointegrated screw-shaped dental implants to anchor a distraction device. Block, M. S., Chang, A., and Crawford, C. Mandibular alveolar ridge augmentation in the dog using distraction osteogenesis. The Journal of Oral and Maxillofacial Surgery. Vol. 54, pp. 309-314, 1996. Furthermore, screw-shaped dental implants alone have been employed to elevate a rectangular osteotomy created in the jaw bone of dogs Ueda, M., Sawaki, Y., and Oda, T. Ridge augmentation by distraction osteogenesis using osseointegrated implants. Abstract. The International Journal of Oral and Maxillofacial Implants. Vol. 13, Nr. 2, pp. 289-290, 1998.
The foregoing references describe two separate and distinct procedures; firstly, osseointegration and secondly, the augmentation of bony defects by distraction osteogenesis. Moreover, during the movement of bone in the direction of distraction, as disclosed in this prior work, the implant is continuously turned in the segment of bone being moved, with integration of the implant occurring only after distraction has been completed.
The use of dental implants in jaw bones where there is no need to augment the existing bone structure is now well-known. Various forms of implant have been created which rely on the growth of bone tissue in and around the implant to create a long lasting, mechanical union between the implant and the natural supporting bone. It is well-known that two primary bonding mechanisms can effect such osseointegration. These are microscopic bonding between the bone tissue and the implant surface and macroscopic ingrowth of bone into interstices of the implant to create a mechanical locking effect. One recent patent discussing such implants is U.S. Pat. No. 5,766,009 issued Jun. 16, 1998 entitled Elastically Stabilized Endosseus Dental Implant.
Thus, there is now a body of knowledge relating to the use and integration of dental implants. Some work has been done in the field of distraction osteogenesis. The two fields have been worked in independently.
Accordingly, within the field of orthopaedics it would be desirable to have a device which enables osteogenesis to occur by distraction to rebuild bone tissue at a particular site. It would also be desirable to have a distraction device which may serve as an anchor for a prostheses following completion of the distraction osteogenesis. This would reduce risk, discomfort and overall cost to the patient.